The present invention relates to a magneto-optical recording material in or from which information is written, read and erased with a laser beam, and more particularly to a magneto-optical recording material which has a high corrosion resistance and a great magneto-optic effect well suited to enhance a readout signal to noise ratio (S/N or C/N).
Recently, the magneto-optical recording which affords a high recording density as well as a large memory capacity and which is capable of, e. g., random access to and erasure of information has come into the limelight. In the magneto-optical recording, a magnetic thin film having an easy axis of magnetization in a direction perpendicular to the plane of the film (a perpendicularly magnetized film) is used, and reverse magnetized domains are formed at any desired positions with a light beam, whereby binary data of "1" and "0" are written in correspondence with the senses of the magnetizations. On the other hand, the binary signals subjected to such reverse magnetized writing are usually read out by exploiting the polar Kerr effect or the Faraday effect.
As the magneto-optical media, there have heretofore been proposed perpendicularly magnetized films such as an MnBi crystalline film, a rare-earth - transition metal amorphous film and a garnet single-crystal thin film. Among them, the rare-earth - transition metal amorphous thin film is deemed the most promising at present for the reasons that medium noise is low due to the absence of a grain boundary and that a large homogeneous area is easily prepared. As the rare-earth - transition metal amorphous thin films, Fe-based alloy systems including Fe-Tb, Fe-Gd, Fe-Tb-Gd and Fe-Tb-Gd-Dy or ones in each of which Fe in an amount smaller than 50 at.% is replaced with Co (that is, the Fe content is larger than the Co content), such as Fe-Co-Gd Fe-Co-Dy, Fe-Co-Tb, Fe-Co-Tb-Gd and Fe-Co-Dy-Tb, and Co-based alloy systems including Co-Gd, Co-Tb, Co-Gd-Tb and Co-Tb-Dy are presently under research as disclosed in, for example, the Official Gazettes of Japanese Patent Application Laying-open No. 52-31703, Japanese Patent Application Publication No. 57-34588, Japanese Patent Application Laying-open No. 56-126907, Japanese Patent Application Laying-open No. 57-94948 and Japanese Patent Application Laying-open No. 58-73746. In addition, the Kerr rotation angle in the residual magnetization of the film itself has been enhanced to approximately 0.35.degree. (at a wavelength of 633 nm).
However, Kerr rotation angles or Faraday rotation angles attained with these prior-art alloy systems are insufficient for producing a readout signal level for practical use, and enhancement in the magneto-optic effect of the film itself for raising the S/N ratio still more is needed. As regards overall characteristics required of the magneto-optical recording media, the Fe-based recording films have such disadvantages that when the Kerr rotation angle .theta..sub.k enlarges, the Curie temperature T.sub.c rises in the extreme, so the recording sensitivity lowers, that the lifetime is short due to an inferior corrosion resistance, and that the crystallization temperature is somewhat low, so stable characteristics are not ensured. On the other hand, the Co-based recording films have information recorded by utilizing the property of the presence of a compensation temperature T.sub.comp and therefore exhibit a high recording sensitivity, but they have the disadvantages that the thermal stability is inferior and that the Kerr rotation angle .theta..sub.k is insufficient.